In the state of the art, flanged bearing-hub assemblies for motor-vehicle driving wheel applications are known. An example is described in the European patent EP 1031439 B1, such embodiment comprising a radially outer ring, a pair of radially inner rings and two rows of rolling bodies (in the example, spheres), radially interposed between the outer ring and the pair of inner rings. The outer ring has an external cylindrical surface, suitable for press fit operations, to insert the bearing into a cylindrical seat, formed in a suspension knuckle. The radially inner rings are press fit on a flanged hub, which is angularly connected in a known way with the end portion of a spindle, in other words an axle shaft of a motor-vehicle powertrain. The rings are typically made of high resistance steel for rolling bearings, since the ring must support high hertzian loads, which are transmitted between rolling bodies and raceways.
The bearing-hub assembly also comprises a hub, which has a flange portion inside of which holes are provided for a plurality of fastening means (for instance, bolts), which connect in a known way an element of the motor-vehicle wheel, for example the brake disc, to the flanged hub.
The flanged hub can also be defined as assembly structural portion, since it supports loads transmitted by the element of the motor-vehicle wheel. Advantageously, the flanged hub can be made of light alloy, anyway of a lighter material than the hertzian portion material, in order to decrease the assembly overall weight. According to state of art teaching, the hub can be co-molded to the hertzian portion, in other words to a rolling ring.
Several co-molding technologies require the light alloy to be transformed in a state different from the solid state, by means of a light alloy heating. The hertzian portion material has a different thermal behavior with respect to the structural portion material (as known a light alloy, for example aluminum, has a greater thermal dilatation than the steel one). Therefore, particularly in applications with a hub rotatable and steadily engaged to the bearing inner ring, it is particularly difficult to ensure that the two portions remain perfectly adherent each other, that is to say, they do not disjoin neither after cooling nor during working operations.